<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /*
      选中处于某种状态的元素
       ● :link      a 标签 未访问过
       ● :visited   a 标签 已访问过
       ● :hover     鼠标悬浮在元素上
       ● :active    鼠标点击元素
       ● :focus     元素获得焦点
     */
    :link {
      color: red;
    }

    :visited {
      color: orange;
    }
  </style>
</head>

<body>
  <a href="#">Hello world!</a>
</body>

</html>